Prevention of cavitation

Abstract

This disclosure relates to a system for reducing cavitation at a surface that moves relatively with respect to a first fluid. The system comprises a degasser configured to at least partially degas a second fluid. The system also comprises a reservoir in communication with the degasser and configured to house the at least partially degassed second fluid, the reservoir having an outlet that is arranged for directing the second fluid towards the surface. The system is configured such that the directing of the at least partially degassed second fluid towards the surface forms a boundary layer at the surface. The boundary layer is adapted to at least partially increase the negative pressure required to initiate cavitation at the surface so as to reduce the occurrence of cavitation during such relative movement.

The invention claimed is: 
     
       1. A method for reducing cavitation at a surface that moves relatively with respect to a first fluid, the method comprising:
 directing a second fluid that is at least partially degassed towards the surface such that the second fluid is able to form a boundary layer at the surface, whereby the boundary layer at least partially increases a negative pressure required to initiate cavitation at the surface so as to reduce cavitation when the surface moves relatively with respect to the first fluid; and 
 wherein the second fluid is periodically directed to the surface using a pulsed flow to form the boundary layer. 
 
     
     
       2. A method as claimed in  claim 1 , wherein the second fluid is degassed by more than 50% relative to a gas-equilibrated form of the second fluid. 
     
     
       3. A method as claimed in  claim 2 , wherein the second fluid is degassed by more than 80% relative to a saturated form of the second fluid at any pressure. 
     
     
       4. A method as claimed in  claim 1 , wherein the second fluid is directed towards the surface at a first volumetric flow rate. 
     
     
       5. A method as claimed in  claim 4 , wherein the first fluid is directed towards the surface at a second volumetric flow rate, with the first volumetric flow rate being up to 50% of the second volumetric flow rate. 
     
     
       6. A method as claimed in  claim 1 , wherein the second fluid is directed to a first region of fluid adjacent to the surface comprising reduced fluid pressure relative to other regions adjacent to said surface. 
     
     
       7. A method as claimed in  claim 1 , wherein the second fluid is delivered through a conduit having an outlet that opens into the first fluid. 
     
     
       8. A method as claimed in  claim 1 , wherein the surface is arranged on or forms a part of at least one of a propeller, hydrofoil, impeller, piston, valve body, restriction valve, orifice or piping. 
     
     
       9. A method as claimed in  claim 1 , wherein the second fluid is a degassed form of the first fluid. 
     
     
       10. A method as claimed in  claim 1 , wherein the first fluid and/or the second fluid is an aqueous solution. 
     
     
       11. A method as claimed in  claim 1 , further comprising operating a flow controller to control a flow of second fluid directed towards the surface to form the boundary layer. 
     
     
       12. A system for reducing cavitation at a surface that moves relatively with respect to a first fluid, the system comprising:
 a degasser configured to at least partially degas a second fluid, wherein the second fluid is periodically directed to the surface using a pulsed flow to form the boundary layer; 
 a reservoir in communication with the degasser and configured to house an at least partially degassed second fluid, the reservoir having an outlet that is arranged for directing the second fluid towards the surface; 
 wherein the system is configured such that directing the at least partially degassed second fluid towards the surface forms a boundary layer at the surface, whereby the boundary layer at least partially increase a negative pressure required to initiate cavitation at the surface so as to reduce cavitation when the surface moves relatively with respect to the first fluid. 
 
     
     
       13. A system as claimed in  claim 12 , wherein the degasser is configured to degas the second fluid by more than 50% relative to a gas-equilibrated form of the second fluid. 
     
     
       14. A system as claimed in  claim 13 , wherein the second fluid is degassed by more than 80% relative to a saturated form of the second fluid at any pressure. 
     
     
       15. A system as claimed in  claim 12 , wherein the system is configured to direct the second fluid towards the surface at a first volumetric flow rate. 
     
     
       16. A system as claimed in  claim 15 , wherein the first fluid moves relatively at a second volumetric flow rate, with the first volumetric flow rate being up to 50% of the second volumetric flow rate. 
     
     
       17. A system as claimed in  claim 12 , wherein the outlet is positioned at a first side of the surface in use adjacent to fluid of reduced pressure relative to other sides of said surface. 
     
     
       18. A system as claimed in  claim 12 , wherein the surface is arranged on or forms a part of at least one of a propeller, hydrofoil, impeller, piston, valve body, restriction valve, orifice or piping. 
     
     
       19. A system as claimed in  claim 18 , wherein the outlet is provided on or at the propeller, hydrofoil, impeller, piston, valve body, restriction valve, orifice or piping. 
     
     
       20. A system as claimed in  claim 12 , wherein the outlet is provided towards or at an end of a conduit. 
     
     
       21. A system as claimed in  claim 12 , further comprising a flow controller in communication with the reservoir for controlling a rate of flow of second fluid to be directed towards the surface.